This invention relates generally to light emitting devices and more particularly to side emitting light emitting diodes (LEDs).
FIG. 1A illustrates a conventional LED package 10. LED package 10 has a hemispherical lens 12 of a type well-known in the art. Package 10 may also have a reflector cup (not shown), in which an LED chip (not shown) resides, that reflects light emitted from the bottom and sides of the LED chip toward the observer. In other packages, other types of reflectors reflect the LED chip""s emitted light in a particular direction.
Lens 12 creates a field of illumination 14 roughly along a longitudinal package axis 16 of LED package 10. The vast majority of light emitted from an LED package 10 with a hemispherical lens 12 is emitted upwards away from LED package 10 with only a small portion emitted out from the sides of LED package 10.
FIG. 1B illustrates a known light emitting diode (LED) package 30 with a longitudinal package axis 26. LED package 30 includes an LED chip 38, a lens 32 with straight vertical sidewall 35 and a funnel-shaped top surface 37. There are two main paths in which the light will travel through package 30. The first light path P1 is desirable with the light emitted from chip 38 and traveling to surface 37 where total internal reflection (TIR) causes the light to exit through sidewall 35 at approximately 90 degrees to the longitudinal axis. The second light path P2 is light emitted from chip 38 towards sidewall 35 at an angle causing TIR or a reflection from sidewall 35 causing the light to exit package 30 at an angle not close to perpendicular to the longitudinal axis. This path is not desirable and limits the efficiency of side extracted light.
FIG. 2 illustrates the conventional LED package 10 of FIG. 1 coupled along an edge of a portion of a refractive light guide 20. LED package 10 is positioned on the edge of light guide 20 along the width of light guide 20. Light rays R1, R2, R3 emitted by LED package 10 are propagated along the length of light guide 20. FIG. 3 illustrates a plurality of conventional LED packages 10 positioned along the width of light guide 20 of FIG. 2. These conventional LED/light guide combinations are inefficient as they require a large number of LED packages 10 to illuminate the light guide and result in coupling inefficiencies due to relatively small acceptance angles. These conventional LED packages 10 must be arranged along the entire length of one side of light guide 20 to fully illuminate light guide 20.
A need exists for an LED package to couple efficiently to shallow reflectors and thin light guides. A need also exists for an LED package to allow these secondary optical elements to have relatively large illuminated areas.
In accordance with one embodiment, a lens comprises a bottom surface, a reflecting surface, a first refracting surface obliquely angled with respect to a central axis of the lens, and a second refracting surface extending as a smooth curve from the bottom surface to the first refracting surface. Light entering the lens through the bottom surface and directly incident on the reflecting surface is reflected from the reflecting surface to the first refracting surface and refracted by the first refracting surface to exit the lens in a direction substantially perpendicular to the central axis of the lens. Light entering the lens through the bottom surface and directly incident on the second refracting surface is refracted by the second refracting surface to exit the lens in a direction substantially perpendicular to the central axis of the lens.
The inventive lens may be advantageously employed to provide side-emitting light-emitting devices that may be used with light guides and reflectors that have very thin profiles and/or large illuminated areas.
In accordance with another embodiment, a light-emitting device comprises a light-emitting semiconductor device and a lens. The lens comprises a bottom surface, a reflecting surface, a first refracting surface obliquely angled with respect to a central axis of the lens, and a second refracting surface extending as a smooth curve from the bottom surface to the first refracting surface. Light emitted by the semiconductor device, entering the lens through the bottom surface, and directly incident on the reflecting surface is reflected from the reflecting surface to the first refracting surface and refracted by the first refracting surface to exit the lens in a direction substantially perpendicular to the central axis of the lens. Light emitted by the semiconductor device, entering the lens through the bottom surface, and directly incident on the second refracting surface is refracted by the second refracting surface to exit the lens in a direction substantially perpendicular to the central axis of the lens.
The inventive light-emitting device may be efficiently coupled to shallow reflectors and to thin light guides. Secondary optics employed with the inventive light-emitting device may have relatively large illuminated areas.
In accordance with another embodiment, a lens cap comprises a bottom surface attachable to a lens, a reflecting surface, a first refracting surface obliquely angled with respect to a central axis of the lens cap, and a second refracting surface extending as a smooth curve from the bottom surface to the first refracting surface. Light entering the lens cap through the bottom surface and directly incident on the reflecting surface is reflected from the reflecting surface to the first refracting surface and refracted by the first refracting surface to exit the lens cap in a direction substantially perpendicular to the central axis of the lens. Light entering the lens cap through the bottom surface and directly incident on the second refracting surface is refracted by the second refracting surface to exit the lens cap in a direction substantially perpendicular to the central axis of the lens cap. The inventive lens cap may provide advantages similar to or the same as those described above.